1. Field of the Invention
The invention relates to image processing, and more particularly, to a method and apparatus for adaptive selection of YC separation.
2. Description of the Related Art
When an input composite video signal is received at a television set, a luminance (Y) signal and a chrominance (C) signal need to be separated out. This process is called YC separation. The luminance signal has a bandwidth of 0˜5.5 MHz. For PAL-I, the chrominance signal is modulated on a subcarrier frequency of 4.43 MHz and for NTSC the chrominance signal is modulated on a subcarrier frequency of 3.58 MHz.
In general, conventional YC separation is divided into three modes as follows. (1) 1-D YC separation: a filter is used to separate each horizontal scan line into Y signals and C signals. (2) 2-D YC separation: adding/subtracting processing (two-dimension YC separation) is performed on signals based on correlation between scan lines (usually within a field) within a frame. (3) 3-D YC separation: the concept of 3-D YC separation is very similar to that of 2-D YC separation, but the 3-D YC separation is based on correlation between frames.
Based on correlation between pixels transmitted in sequence within a frame, or variation of pixels in the vertical direction and horizontal directions within the frame, conventional YC separation methods are used to design an adaptive separation filter. However, in the case where a sampling frequency of a signal is deviated, conventional adaptive YC separation methods are unable to effectively determine whether the sampling frequency is deviated such that the adaptive separation filter may perform 3-D inter-frame YC separation on the signal, thereby obtaining a poor image quality. Consequently, there are problems in how to effectively determine whether the sampling frequency of the signal is deviated or a sampling point is shifted, and in how to select a suitable YC separation mode if the sampling frequency of the signal is deviated.